1. Field of the Invention
The present invention relates to a magnetic field sensing element for detecting a change in a magnetic field, and more particularly, to an element used in a device for detecting the number of rotations of, for example, a gear-like magnetic rotating body.
2. Description of the Related Art
FIG. 26 is a partial enlarged view of an essential portion of a conventional magnetic field sensing device.
FIGS. 27 and 28 are a sectional side elevation and a bottom view, respectively, showing the internal structure of the conventional magnetic field sensing device. It is to be noted that the bottom view of FIG. 28 shows the magnetic field sensing device of FIG. 27 with its case removed.
As shown in FIG. 26, the conventional magnetic field sensing device comprises a magnetic field sensing device body 1 and a connector 2 connected with the magnetic field sensing device body 1.
As shown in FIG. 27, the magnetic field sensing device body 1 comprises a cylindrical case 3 made of synthetic resin, an electric circuit body 4 housed in the case 3, a rectangular-parallelopiped-shaped permanent magnet 5 provided at an end portion of the electric circuit body 4 (on the right side in FIG. 27), and a magnetic field sensing element 6 provided on the front surface of the permanent magnet 5 with a built-in giant magnetic resistance element (hereinafter referred to as a GMR element).
Further, as shown in FIG. 28, the electric circuit body 4 comprises a substrate 7 made of synthetic resin, resistors 8 and capacitors 9 provided on the substrate 7, and wiring 10 for electrically connecting the resistors 8, the capacitors 9, and the magnetic field sensing element 6.
In the above-mentioned magnetic field sensing device, rotation of the gear-like magnetic rotating body 11 provided in proximity to the magnetic field sensing element makes concavities 11a and convexities 11b of the magnetic rotating body 11 alternately approach the magnetic field sensing element 6, and thus, cause a change in the magnetic field of the permanent magnet 5 applied to the magnetic field sensing element 6.
This change in the magnetic field is detected as a change in voltage by the GMR element (not shown) inside the magnetic field sensing element 6. The change in voltage thus generated in the GMR element is output via a differential amplification circuit and a comparison circuit both in the magnetic field sensing element 6, to the outside as a pulse wave electric signal. This electric signal is transmitted via a terminal of the connector 2 to a computer unit (not shown) which calculates the rotation angle of the magnetic rotating body 11. It is to be noted that the resistors 8 and the capacitors 9 form a filter circuit which prevents external noise, including external surges, from penetrating to the magnetic field sensing element 6.
In the conventional magnetic field sensing element, since a lot of time is required to solder the resistors 8 and the capacitors 9 to the substrate 7, there is a problem in that the production efficiency of the magnetic field sensing device is low and the manufacturing cost is high.
Further, since space is required for assembling the resistors 8 and the capacitors 9 on the substrate 7, there is a problem in that the size of the magnetic field sensing element and the magnetic field sensing device as a whole accordingly become larger.